Proper alignment of a power transmitting belt and its belt idler is important to the life of the drive components, particularly the belt. This is especially true of a system wherein a flanged idler with a cylindrical belt engaging surface is used to engage the backside of a V-belt. If the belt rides against either flange, it will cause excessive belt side wear, and may cause the belt to turn over in the pulleys which adversely affects the internal load carrying structure of the belt. Historically, spring loaded idlers have presented alignment problems. The idler arm is often a weldment and also the mounting bracket for the idler arm may be a weldment. There is inherent warpage in welding components to one another and thus some means of compensating for the manufacturing tolerances is desirable in order to provide proper axial alignment of the idler pulley with the belt it engages. Another cause of idler misalignment is the tolerance build-up in the pulley, the idler arm and its mounting structure, which may result in the axis of the idler being out of parallelism with the backside of the belt. This will cause the belt to move in one axial direction or the other on the cylindrical face of the idler pulley.
One prior art arrangement for adjusting the axial position of the belt idler is illustrated in FIGS. 1 and 2. In addition to being rather expensive, this prior art adjusting arrangement is rather cumbersome and is not suitable for adjusting the idler when it is hidden behind a wall or panel, and, further, it is not suitable for adjustment during the running of the belt because of the inherent danger in performing the adjustment in close proximity to a running belt.